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James Duff hydroboost Mastercylinder?

Desert Thrasher

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Does anyone know what mastercylinder JD uses in their hydroboost kit? It is low profile and has an almost flat cap. Which is what I need to complete my hydroboost install. Here is a pic of it.
 

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toddz69

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Desert Thrasher said:
Does anyone know what mastercylinder JD uses in their hydroboost kit? It is low profile and has an almost flat cap. Which is what I need to complete my hydroboost install. Here is a pic of it.

77-82 Corvette.

Todd Z.
 
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Desert Thrasher

Desert Thrasher

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PAPITT said:
DID YOU ask enough questions ...do you have disk and disk brakes ...

I have disk brakes up front and drums in the rear. What is the vette MC for?
What size bore does it have?

I dont know what hydro unit the JD kit uses. I asked them but all they could tell me was where they bought the complete kit from. Thats why I just went here for the info on the MC.
 

Apogee

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The Corvette master cylinder from a 1977-1982 model is an AC Delco #18M91, has an 1-1/8" bore, and is designed for a disc/disc system. If you choose to use it in a disc/drum application, you'll want to add a 10# residual valve to the rear line to keep the shoes close to the drums. There are probably better MC choices for a disc/drum setup that will save you the expense of thet residual valve...however if you're going to convert the rear to discs in the future anyways, it may not be a bad choice.
 

toddz69

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daddyg said:
So the kit James Duff sells is an Astro unit? Just curious

No, it's the internal accumulator unit used on various GM cars in the early '80s.

Todd Z.
 

toddz69

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Desert Thrasher said:
I have disk brakes up front and drums in the rear. What is the vette MC for?
What size bore does it have?

I dont know what hydro unit the JD kit uses. I asked them but all they could tell me was where they bought the complete kit from. Thats why I just went here for the info on the MC.

If you have discs/drums and will keep it that way for awhile, I'd get the 10# residual pressure valve that someone else mentioned, or use a '79 Camaro master cylinder. It's already set up for disc/drums.

Everything I've seen of Duff's units tells me they're buying them from Vanco.

Todd Z.
 

Pa PITT

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I wasn't completely sure but I did think the vette was for disk and disk ...and the disk drum set up used like one said camaro or I think some of the guys use
ford tr with 1 1/8 cyl ...but if you look around like auto zone ""cheap stuff"" about 25.00 each ....how bad is 25.00 to change cyl if you go to disk on the rear ..
 
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Desert Thrasher

Desert Thrasher

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I already have a F250 mastercylinder, it was too tall so I milled about 1/2" off, it clears now but the cap doesnt. I plan on just making a new mounting plate that will lower the whole hydro unit down another inch or so.
 

Apogee

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toddz69 said:
...or use a '79 Camaro master cylinder. It's already set up for disc/drums.

Just to clarify, there are two master cylinders available for the 1979-1981, one for power brakes (ACD#18M18, 1-1/8") and one for manual (ACD#18M76, 1"). Obviously, the power brake version is the one to consider for a Hydroboost setup.
 

toddz69

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Apogee said:
Just to clarify, there are two master cylinders available for the 1979-1981, one for power brakes (ACD#18M18, 1-1/8") and one for manual (ACD#18M76, 1"). Obviously, the power brake version is the one to consider for a Hydroboost setup.

Yes, I should've clarified that.

Todd Z.
 

Pa PITT

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WHAT ARE THOSE NO.S are they ford parts no. I dont reconized them...
how about raybestos or wagner or cardon A1....no.s......
 

Apogee

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PAPITT said:
WHAT ARE THOSE NO.S are they ford parts no. I dont reconized them...
how about raybestos or wagner or cardon A1....no.s......

Sorry about that PAPITT...ACD = AC Delco. Here's the cross reference info as requested. I don't know the Wagner numbers off hand.

1-1/8", disc/drum, power brakes, GM:
ACD #18M18
Raybestos PG+ #MC36306
A1 Cardone #101521
Note: 1968-1995 midsize cars and were probably one of the single most common master cylinders GM ever used.

1" bore, disc/drum, manual, GM:
ACD #18M76
Raybestos PG+ #MC39023
A1 Cardone #101612
Note: 1975-1980 GM midsize cars
 

Vancopbs

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If your Bronco came with 2 wheel disc then your prop valve has the residual valve built in, adding a 10 lb valve is doubling it.

You have the master correct if you went to an Auto part store. I actually use a quad port, GM/Ford Deep/Shallow piston master designed off the Corvette. All that means is I can mount the master to anything with lines going to the engine or the wheel well. It's your 2 wheel disc or 4 wheel disc proportioning valve that matters, not this master.

I switched Duff over to an Astro Van like booster. In other words, the external accumulator. The boosters are actually 2000+ 1 ton Chevy trucks.
 

Madgyver

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Vancopbs said:
It's your 2 wheel disc or 4 wheel disc proportioning valve that matters.

Is there a difference between 2 wheel disc PVs and 4 wheel disc PVs?

I am currently using the stock ford 77 Bronco proportioning valve with a 78 Vette MC, 4 wheel discs, Front T-Bird calipers and rear Cadillac calipers.

I have recently installed an adjustable Proportioning valve in the rear lines but still cannot lock up the front discs even with the rear line pressure reduced.

What gives?
 
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